import java.util.Scanner;//1043: 【入门】行李托运价格

public class Main1043 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double a = sc.nextDouble();
        if (a <= 10.00) {
            System.out.println("2.50");
        } else {
            double n=2.50+1.50*(a -10.00);
            System.out.println(String.format("%.2f",n));
        }
    }
}